


Once You Swap You Can't UnderStop

by Tically



Series: That's Undertail, baby! [2]
Category: Undertale (Video Game)
Genre: Honeypuppy - Freeform, M/M, Overstimulation, Puppyberry, Swapcest - Freeform, dubcon, noncon, papcest - Freeform, swapfellcest - Freeform
Language: English
Status: In-Progress
Published: 2019-01-08
Updated: 2019-01-08
Packaged: 2019-09-13 11:54:48
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 8
Words: 2,828
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16892115
Author URL: https://archiveofourown.org/users/Tically/pseuds/Tically
Summary: Horny ficlets with Swap bros, Swapfell bros, and permutations of the two.one big excuse to project sexual fantasies onto Blueberry





	1. Swapfell Overstim

**Notes for the Chapter:**

> Swapfell

In the early morning hours, Sans crawls into Papyrus’s bed. Pap stirs, asks what’s wrong. Sans touches their foreheads together and wordlessly begins rubbing him off.

Pap is confused, but after its clear Sans isn’t going to talk about this, he relaxes into it and lets himself be pleasured.

He comes, very close to kissing Sans, and he basks in the afterglow for a minute before Sans starts up again.

Pap yelps and with a nervous chuckle lets Sans know that’s a bit sensitive maybe wait a little bit…maybe, he says, reaching towards Sans, let me service you…?

Sans slaps his hand away harshly, still without a word.

Papyrus shakes the sting out of his carpals and tries to move past the discomfort, but his body is twitching quite a bit.

Soon, the stimulation turns to pleasure once again, and he moans into it and wills himself toward another orgasm. He grips onto Sans’ arm as he comes.

Pap lays there panting, and whines and pushes Sans away when he once again starts to rub his bones. It’s downright painful, this time.

Sans grabs his wrists and slams them down to the hips, causing Pap to cry out in distress.

Sans moves down Pap’s body and starts lavishing his tongue along the pelvic bones with reckless abandon.

Pap is caught in a horrible whirlpool of pleasure and pain. Sans is keeping a grip on him, threading his phalanges through Pap’s radius and lower ribs to hold him down.

Papyrus is bucking and crying, it hurts, it huuuuuur–uhhhgood. Fuhhhck, oh fuck right there, S-Sans–please–can’t–

He arches and comes with a choked shout, then crumples to a limp pile. Please, he begs, his voice pathetically weak, no more. Please, stop. I’ll do anything.

Sans lifts his head to stare blankly at his brother. A blue tongue slips out to clean the magical residue off his teeth. He watches Papyrus’s ashen face for the reaction as he lowers his pajamas to reveal his cock. Sans takes a moment to enjoy the blue glow washing over his brother’s frightened expression.

He smirks. “No.”

**Notes for the Chapter:**

> 11/18/2016


	2. Swapfell Pap teases Underswap Sans

Blue is transfixed as this monster that looks so much like his brother slides to their knees in front of him. He tugs at his scarf nervously from his seated position on the bed.

“i _live_ to serve you,” that so familiar voice purrs, tinged with a sultriness that Sans has never heard before. Eyelights burning in a way he’s never imagined. It makes a warmth stir in his gut.

The not-brother spreads Sans’s legs apart sensually, still watching him intensely. “you have but to ask,” he murmurs, and runs his gloved phalanges along the inside of those thighs.

The way this Papyrus carries himself promises pleasure with every motion. Sans feels more than a little wrapped up in the moment, caught in a web with no escape. His breath hitches as the other skeleton rests his skull upon Sans’ knee and smirks up at him.

“please, m'lord,” the skeleton moans, eyesockets closing, bucking his hips forward just a bit in a show of wanton desire. Sans can feel the monster’s intent to mate filling up the room with a staticy charge of magic potential, and it’s sending a flare of **want** through his foggy mind.

Dazed eyelights meet lidded sockets brightly glowing orange. “command me. bend me to your will,” the not-Pap _(not Papy, he is not Papy)_ groans with _need._ He is rubbing Sans’s femurs close to his pelvis, now, and Sans’s breath is catching over and over until his sockets slide closed and he lays back on the bed.

The other Papyrus snakes up between his legs and leans over Sans, elbows resting on either side of his skull. “Your orders, m'lord?” Sans shivers visibly as the low, rumbling voice and vivid smell of _heat_ brings his body to involuntarily swirl magic between his legs. He squeezes the Papyrus between his femurs, forgetting his position entirely for a moment.

“K-KISS ME,” he whimpers, mind too hazy to articulate anything else.

“oh?” The other Papy runs his teeth lightly along Sans’s jaw. “where, my lord, would you like this kiss?” He clanks Sans on the mandible. “here?” On the clavicle. “here? or…” he trails off, moving down the younger skeleton’s body, and soaking up how the little one quakes with anticipation.

“do you want it” he presses his teeth to San’s dampened shorts, voice lowered to a deep growl, “ **here**.”

**Notes for the Chapter:**

> 12/18/2016


	3. Black Hole

**Notes for the Chapter:**

>  **Spoilers** for Blue Gets Tortured by Vidoxi. Takes place in post-BGT Swapfell universe. Big angsty.

Papyrus grovels on his stomach, clinging to Sans’s leg for dear life “for but a drop of your affection, my lord-”

Sans face twists into a sneer of disgust. He doesn’t understand where his sudden boiling-over revulsion and fury comes from. He kicks his brother square in the face. He doesn’t even feel satisfaction at the ensuing crack under Papyrus’s eye socket.

“Ugh, you’ve gotten blood on my boot, mongrel.” Sounds disinterested, almost. Mostly just _angry._

Papyrus, bleeding freely, tongue bathes the offensive liquid off of the shoes, prostrate still. Occasionally lets out a whimper of pain. The blood keeps flowing and he keeps laving.

It’s not enough for Sans. Wants to hurt, something about the way the _filth_ wants **tenderness** from him? As if he’d _earned_ such an honor. The urge to break is overwhelming, and he pulls Papyrus’s leash to the point of choking while he instructs the cur to suck him off. The whole time, he’s just _frustrated_ and tells Papyrus how _bad_ he is at this.

He’s cruel, but never in the way they were in the “past life,” because part of him is Blue, and Blue can’t be evil, no matter the loss of innocence. He just withholds love and _gives_ **pain** and always, he is nurturing a cage of black resentment around his soul.

He flies off the handle at any insinuation of Papyrus being “unfaithful” to him, and murders those monsters who manage to get close. Once, some wayward well-meaning soul had tried to intervene in Sans’s more public punishments. The message their slowly draining HP had given as they shrieked for mercy had dissuaded the crowd from further interruptions.

And he _really_ takes it out of Papyrus’s ass afterward. Papyrus is _his,_ body, mind, soul. (His to torture for reasons he doesn’t understand and also his to love because that was always, always on the table.)

Papyrus really doesn’t stray, though. He’s _obsessed_ with Sans. He craves some sort of closeness, though he knows he doesn’t deserve it. He feels that he belongs with Sans, _yearns_ for an intimacy he knows is possible (that his soul knows he’s lost), and the maybe-guilt he was “born” with (neither of them remember how they got to Snowdin) keeps not much room in his head for anything but his lord.

I HATE YOU, his enslaver would say, punching him in the face while Papyrus sits slouched on his knees, arms limp at his sides.

I LOVE YOU, his enthrallment would sob, clinging onto him for dear life as he rides out the fifth orgasm of the night.

Sans doesn’t understand it.

He beats him to near dusting and stalks away furiously because it isn’t enough. He throat fucks him roughly and shoves his skull, leaking cum from every orifice, to the ground, and is _frustrated_ because it _isn’t enough._ He bites into the mutt’s soul and pours every ounce of _contempt_ for his brother into the connection and **screams** because it _ISN’T ENOUGH._

Sans may be living out his karmic retribution, but he will never know peace until his soul forgives his brother for the atrocities that were committed to it.

**Notes for the Chapter:**

> 12/6/2016


	4. Puppy

_Hold me back. Tame me. I’m a voracious beast of excess, and I need your control. My lord, I crave it– **bend me to your will, or else.**_

_Or else this hunger will overtake me, entirely. Beat me into submission before I break you just to drink the marrow. Restrict my movement and my words, lest I humiliate the both of us to taste your tears. **Hurt me** , let me feel that **delicious sting** –it feels so much better when it comes from you–because I know my lord does not share my inclinations. And if you don’t…_

**Notes for the Chapter:**

> These are just his horny thoughts. He’s pretty sick, huh?


	5. When the Cat's Away

Black lost composure for a moment, frustration at the other finally overcoming his earlier promise to be nice while visiting this world. He could stand this sideshow no longer.

“You’re a laughing stock and you’re too dense to even know it!”

Blue’s smile froze, eyelights narrowing slightly at the other.

An awkward silence fell over the four of them, Stretch glaring at the two small skeletons and Slim watching Stretch for unsavory reactions.

But it was unnecessary as Black took a closer look at Blue’s expression. “No,” he said slowly, noticing for the first time a familiar haughty fire in the other’s eyelights. “You do, don’t you?”

He stood up snappily and grabbed a surprised but unflinching Blue by the arm. “Come, no double of mine is going without proper training.”

Stretch moved as if to stop them, but Slim shot a firm hand out to grip his arm.

“You can trust him,” is all he said.

Stretch settled back down.

...

 

“You see traces of your real self in me, don’t you?” Slim brushed his fangs against his copy’s jaw, loosely placing an arm around his waist. His next words were nearly a moan: “I’m sure you’d do _anything_ for him, if only he’d ask.” The answering shudder said enough.

“Admit it,” he continued, pulling back to shoot a sultry look into Stretch’s eyes. “You’re jealous of what I have.” Leaning in close, voice reduced to a whisper, their mouths a hair’s breadth from connecting. “A Sans who demands to be touched, the way you–”

Brushed, teeth to teeth, “ **want** –”

A hot tongue slithered across Stretch’s mouth, their bodies now flush against one another, “to be touched.”

Slim invaded his counterpart’s mouth with an ecto tongue, gripping him fully, and Stretch melted into the embrace with no resistance, entirely too turned on to question it.


	6. Swap's Favorite Things

Stretch’s first time going down on Blue, he really takes his time driving him crazy. Kisses to the lips, slow descent into licking him. Works his tongue in between the folds bit by bit, teases the entrance with his fingers before finally, hooking an arm fiercely around a writhing, very vocal Blue’s leg to press on the mound (and hold him down) while working his fingers up against his spot and sucking on the sopping wet clit.

Makes him cum incredibly hard, incredibly satisfying.

 

Pap’s subsequent times going down on Blue, he really makes an effort to hear him ask for his cock.

With one hand petting Pap’s skull, and one thrown above his head, Sans moaned deliciously, “Ohhh, you’re so good at this…”

Papyrus smirked and pressed up against the front wall–

“Nnngga! Not there~, Papy you know it just makes me want more.”

“heh. but I like hearing you beg.” Audible wink.

Sans huffed, but breath caught when Pap started a rhythm.

“Oh, oh, nnng, haah, mmmm, you– oh f-for g-goodness saaaaaaaake!”

“mmm, then say it, huh? mmm, gods you taste so good. i could just stay down here a~ll da~y, you know?”

Sans wriggled helplessly in his brother’s grasp and covered his eyesockets in defeat. “Fine, Papy, please stop teeeeasing me. I neeeed you.”


	7. Papys Are Super Narc

Slim backs Stretch up against the wall before sinking to his knees with a playful smirk. He nuzzles the glowing bulge in the other’s pants before winking up at his twin’s conflicted expression. Always teasing, always mocking in his body language. This false subservience gave him a thrill. He felt the most powerful when someone was looking down on him.

And Stretch likes to watch. He keeps eye contact as his scarred double pushes his pants down past his crests. They stare into eachother’s eyes as Slim licks a long, wet stripe up Stretch’s cock.

A silent battle for dominance. Who will crack first and submit fully to their lust?

It’s a mouthwatering sight. But Slim knows every trick and spot on his body–it is identical to his own in magic, afterall–and Stretch’s eyes slide closed when Slim takes him deep into his throat–deeper than anyone has taken him, before. The pleasure is overwhelming, and he tugs on Slim’s jacket as he comes down the monster’s conjured throat.

Slim dispels the magic and comes up for air, gagging and choking, a thick trail of drool leaking out of his mouth. He smirks up at Stretch, who is panting and blearily looking down at him, and pulls his shirt up to show his ribs entirely coated in magic.

Stretch slides down the wall to sit, and they consider eachother for a moment. He catches his breath, then grins and with a “heh,” tackles Slim unexpectedly. Almost cracks his skull on the floor with a yelp of surprise. Stretch shoves his tongue down Slim’s mouth into his vertebrae, tasting his own honey-sweet cum and reaches into the other’s pants to jerk him off quickly, harshly, making his bones chafe against the ground and Slim growls appreciatively at the pain.


	8. Surface Fluff

**Notes for the Chapter:**

> Underswap

Sans adjusted himself to cozy up more to his brother’s side. He could make the excuse that he was cold to get some more cuddling, but Papyrus would see right through that. This mildly biting cool was nothing compared to their home in Snowdin.

Home. He chuckled quietly to himself, idly poking the embers of their campfire. He wondered how long he would still think of the underground as his home.

Papyrus rubbed his teeth to Sans’s skull, enjoying the crisp night air, the smell of ash and the utter quiet around them. “What’s so funny, huh?” he asked quietly.

Sans settled closer, blinked up at the endearing smile playing at the corners of his brother’s mouth. He loved it when Papyrus had that look. It made his soul feel warm. Made him feel wanted. No matter how much he enjoyed the flood of attention the humans had given him, (FINALLY, MY GREATNESS IS RECOGNIZED!) at the end of the day, when he came back home to that smile…

Sans turned his gaze up to the twinkling stars above them before answering.

“Just…wondering if I’ll ever get used to this. There’s so much room; it just–” he gestured widely at the horizon, flapping his arms and causing Papyrus to fumble atputting arm around him to keep him from sliding off their log perch, “–goes on forever an’ ever.”

Sans plunked back down, settling his skull into the crook of Papyrus’s neck and enjoying the closeness.

How long it would take to see this new, open, exciting (scary) place as his home? Would he ever?

For that matter, he thought, sneaking a peak at the stress lines under Papyrus’s sockets, would his brother ever see it that way?

Everyone’s lives had changed so drastically since the barrier was open. For most monsters, there was a giddy expectation (and fear) of a completely blank slate. There was life, glorious life breathed into a once caged and bored population. There was hope, now, and change. Sans had even discarded his battle body, electing to build a newer, more human-aesthetic garb. A move which greatly increased his likes on Instagram.

So why did only Papyrus still look…tired?

_“MY BROTHER, WELL, HE WON’T CHANGE VERY MUCH.”_

When Sans had said those words to the human, he hadn’t been referring to the earth-shattering paradigm shift of moving to the surface.

He had been referring to how Papyrus was a rock to him, always had been. (As stubborn and lazy as a rock, too.) Sans’ dreams coming true wouldn’t change their relationship, and apparently the surface hadn’t, either.

Papyrus pulled a cigarette out of his pocket and lit up.

“Ugh, right now?”

Pap shrugged. “Hey, I love star-gazing as much as you do, but we’ve been out here for almost 2 hours.” He puffed to the side.

“You really need to cut back brother,” he grumbled, crossing his arms petulantly and paying careful attention to the way his brother’s ribs expanded with each inhale. The smoke, he noted, smelled a bit different this time. More cloying, almost sweeter. Like an incense.

“aw, says you.” he said, nuzzling sans once more. “Besides, these surface cigs have a neat little quirk.” Papyrus dipped down and ran his teeth across Sans’s.

Sans let out an undignified squeak, cheeks lit up like a gryftmas tree.

“Alright,” Papyrus said, eyelights sparkling with laughter, and voice strangely breathless. “Now, lick them.”

Still a bit flushed from the sudden affection, Sans cautiously darted his tongue out. His eyelights grew at the flavor of sweetness.

“Heh, it’s nice right? These cigarettes make your mouth taste like sugar.” He pulled another drag.

“Can I–” Sans ducked his head in a rare show of bashfulness. “Try it, again?”

Papyrus eyelights smouldered at him. “Absolutely,” he purred, before dipping in again.


End file.
